Ovalicin is a metabolite of Pseudorotium ovalis possessing antibiotic, antitumor, immunosuppressve, and seed germination stimulating properties. Fomannosin is a phytotoxic metabolite of the economically important wood-rot fungus Fomes annosus. Pentalenolactone is a metabolite of Streptomyces roseogriseus with a broad spectrum of antimicrobial activities, being particularly effective against phytopathogenic fungi. The structure of each of these sesquiterpenes presents a unique and complex biosynthetic problem, not readily amenable to traditional radioisotopic labeling and degradation techniques. The proposed research will examine the biosynthetic problems posed by these substances. The goals are to: 1) elucidate the rearrangement pathway by which ovalicin is formed, and to identify the key intermediates along this pathway; 2) to provide mechanistic and stereochemical details bearing on a proposed scheme for the biosynthesis of fomannosin; 3) to establish a biosynthetic scheme for the formation of pentalenolactone; 4) to examine the application of powerful instrumental techniques, carbon and deuterium magnetic resonance, to biosynthetic problems; and 5) to probe and extend the utility of homo-and heteronuclear double labeling in magnetic resonance studies of isoprenoid biosynthesis.